Flashcards in Meiosis Deck (28):
What is meiosis?
single round of DNA replication followed by 2 consecutive rounds of cell division
Cytokinesis in females is uneven, what is the result of this?
each original 2N oogonia entering meiosis gives rise to only one 1N oocyte at the conclusion of the two meiotic divisions
What are polar bodies?
remnant cells left over after most of the cytoplasm goes to one of the cells during female meiotic division
Describe the first polar body
arises from the first meiotic division in females
Describe the second polar body
arises from the second meiotic division
When does meiotic division stop in females?
first meiotic division is arrested at about the time of birth in most animals
When does reinitiation of the first meiotic division occur in females?
sometime after puberty and is a result of the preovulatory LH surge
What happens when the first meiotic division is reinitiated in females?
-oocyte completes meiosis and first polar body is expelled
-immediately enters the 2nd meiotic division and is arrested
-oocyte arrested in meiotic division is ovulated
When does the 2nd meiotic division occur in females?
when the oocyte is reactivated by a penetrating sperm at time of fertilization
What does the corpus luteum form from?
remnants of the ovulated follicle
Definition of leutinization
When does leutinization occur?
following the LH surge but prior to ovulation, when the follicles begin to secrete less estrogen and more progesterone
What happens to the follicle after ovulation?
-collapsed follicle reorganizes
-granulosa cells form the large luteal cells
-theca cells form the small luteal cells
Function of large luteal cells
-baseline progesterone secretion
-do not respond to LH by increasing progesterone secretion
Function of small luteal cells
-respond to LH by increasing progesterone secretion
What are luteotropins?
hormones that support the CL
Name some luteotropins and their effects (4)
1. LH - responsible for the early changes of luteinization
2. Prolactin - important luteotropin in carnivores, mice, rats, and hamsters
3. Estradiol - luteotropin in rabbits, may be lutolytic in other animals
4. PGI2 and PGE2 - luteotropic in cattle and women
Function of the CL
inhibits the hypothalamo-pituitary axis by its secretion of progesterone
How can a new estrus cycle commence in animals?
CL must be removed (luteolysis)
How does luteolysis occur?
-decreased progesterone influence and increased estrogen influence allows increased oxytocin secretion
-increased oxytocin secretion causes PGFalpha2 release
-PGFalpha2 causes luteolysis of CL
How does luteolysis occur in animals with a closely applied ovarian artery and uterine vein?
prostaglandin from uterine endometrium passes up uterine vein and a portion is transferred across vessel wall into ovarian artery where it can directly access the CL
(sheep and guinea pig)
How does luteolysis occur in animals where the ovarian artery and uterine vein are not closely applied?
prostaglandin is transferred via the systemic circulation, which results in a much less active metabolism in the lungs
(horses and rabbits)
Explain luteolysis in ruminants
prostaglandin release from the uterine endometrium causes oxytocin release from the CL, which causes more prostaglandin release from the uterine endometrium, etc. etc.
Explain luteolysis in primates
central oxytocin release acts on luteal oxytocin receptors which gives local formation of prostaglandins within the CL
What is pseudomenstruation?
blood coming from the vagina without destruction and sloughing of the endometrium at the end of the luteal phase
Why is there bleeding from the bitch during proestrus?
blood cells are lost into the uterine lumen by diapedesis and following rupture of small capillaries
Why is there bleeding from the cow during metestrus?
caruncular capillaries hemorrhage following the rapid decline in estrogen after ovulation